Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials (1999) / Chapter Skim
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4 Role of Exposure and Dose or Drink Assessments in Developing Radiation Standards
4 Role of Exposure and Dose or Drink Assessments in Developing Radiation Standards
Pages 75-88
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From page 75... ...
The chapter ends with the committee's views on suitable approaches to exposure and dose or risk assessments for purposes of developing standards for radionuclides in the environment. RISK ASSESSMENT OF CARCINOGENS As described, for example, by the National Research Council (1983)
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From page 76... ...
However, hazard identification is not an important concern for radionuclides, including naturally occulting radionuclides found in TENORM, because widespread epidemiologic data have shown conclusively that ionizing radiation can cause cancer in humans (for example, National Research Council 1990; 1988~. Noncarcinogenic health effects also are potentially important for some radionuclides that can be found in TENORM.
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From page 77... ...
Current estimates of the dose-response relationships for radiation exposure obtained, for example, by the National Research Council's Committee on the Biological Effects of Ionizing Radiations (National Research Council 1990; 1988) are based on studies of human populations that received radiation doses considerably above environmental levels.
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From page 78... ...
ELEMENTS OF RADIATION RISK ASSESSMENT This section discusses the calculational elements that normally make up an assessment (estimation) of risk posed by exposure to radionuclides in the environment.
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From page 79... ...
However, we are discussing radiation risk assessment separately mainly because the approaches to estimating radiation risks were developed long before the general riskassessment process for carcinogens was formally laid out. Radiation risk assessment usually includes estimates of dose from a given exposure, which are generally not part of risk assessments of chemical carcinogens.
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80 e e "I-~ DIAL ~ ~ : IllllllI1 I F ELIDE T-IO r e : I ~OSU~ 1 -I "OL-1C+ LOGIC DOSE DOS BLOC 1 EuNG .
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From page 81... ...
, but they might not be adequate for estimating doses and risks for real exposure situations (see chapter 11~. The approach to estimating internal and external exposures per unit concentration of radionuclides in various environmental media (the first element of a risk assessment)
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From page 82... ...
82 ROLE OF ASSESSMENTS IN DEVELOPING STANDARDS CONCENTRATIONS | _ IN SOURCE COMPARTMENTS r TRANSPORT AND INTERACTION PROCE SSES CONCENTRATIONS EXTERNAL ~IN EXPOSURE EXPOSURE COMPARTMENTS 1 1 l DOSE TO l I HUMANS | _ INTERNAL EXPOSURE Figure 4.2. Relationships between concentrations of radionuclides in source compartment and resulting doses to humans from internal and external exposure.
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From page 83... ...
For contaminated air, important exposure pathways generally include: · Inhalation and external exposure to airborne radionuclides in the source compartment. · Exposure to radionuclides deposited on vegetation and the ground surface, including external exposure and ingestion of radionuclides incorporated into foodstuffs (vegetables, fruits, grains, meat, and milk)
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From page 84... ...
for the radionuclides, also is important. The models and parameter values for the various internal and external exposure pathways of concern in exposure assessments for radionuclides in the environment are discussed in a number of references (for example, IAEA 1996b, 1994; NCRP 1984d; Till and Meyer 1983~.
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From page 85... ...
If biologic-uptake data are not available, leaching tests with dilute acids to assess readily dissolvable fractions, or salt solutions to assess ion-exchangeable fractions can be used to provide an index of biologic availability. USE OF DOSE OR RISK ASSESSMENT IN DEVELOPING RADIATION STANDARDS In principle, radiation standards expressed in terms of dose or risk can be developed without the need to consider exposure-pathway and dose or risk assessments for the exposure situations of concern.
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From page 86... ...
More generally, dose or risk assessments are important in developing radiation standards because risks posed by environmental exposures are not directly observable and dose often cannot be measured, especially the dose from internal exposure. Dose or risk assessments are important in developing radiation standards in the following ways.
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From page 87... ...
First, in developing radiation standards, it is appropriate to use stylized methods of exposure and dose or risk assessment for assumed reference conditions, provided that the assumed conditions are reasonably representative of the exposure situations of concern and that the regulations permit the use of alternative and more realistic approaches for specific exposure situations, especially in demonstrating compliance with the standards. The use of stylized methods of exposure, dose, and risk assessment in developing environmental standards for radionuclides is consistent with the approach used in developing secondary limits (limits on intakes of radionuclides or concentrations of radionuclides in air)
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From page 88... ...
The need for reasonably realistic assessments is particularly important if standards are based on cost-benef~t analyses with respect to dose or risk. A dose or risk assessment that is unreasonably conservative or nonconservative could lead to standards that either are not reasonably achievable or are not adequately protective of public health.
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